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gh-127833: lexical analysis: Improve section on Numeric literals#134850
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| Instead, :ref:`complex numbers <typesnumeric>` can be written | ||
| as adding the complex number's real part and imaginary part. | ||
| .. productionlist:: python-grammar | ||
| imagnumber: (`floatnumber` | `digitpart`) ("j" | "J") | ||
| For example, the imaginary number 3.1+4\ *i* can be written as adding the | ||
| real number 3.1 to the imaginary number 4\ *i*. |
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Sorry, but this is a wrong picture.
The CPython has no pure-imaginary numbers and above decomposition is invalid in general. Simple counterexample:
>>>-0.0+0j0j>>>complex(-0.0,0)(-0+0j)
Previous description was valid: "An imaginary literal yields a complex number with a real part of 0.0."
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The key point is this islexical analysis. Python indeed has no imaginary literals, but the tokeniser does --4+16j is three tokens.
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I think L1093 should say 'the complex number ...', though.
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Sure, but16j is not an imaginary number. It's a complex number with a real part+0.0. And complex number in the Python currently can't be "written as adding the complex number's real part and imaginary part."
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16j is not an imaginary number; but 16i is :)
I agree that this could be clearer. Will update. (Not surewhen, as I recently volunteered to focus on f-strings first.)
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16j is not an imaginary number; but 16i is :)
But you are talking not about mathematics, but Python's complex numbers.
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Each section is expanded, and now progresses from simple cases and examples to more involved ones, ending with the formal grammar.
This uses meta-syntax that I want to add to the introduction in#134443. I'm marking it as draft until that's merged.
📚 Documentation preview 📚:https://cpython-previews--134850.org.readthedocs.build/